1. Field of the Invention
The present invention relates to a disc loading mechanism that rotatably holds a disc, and a disc drive apparatus that includes the disc loading mechanism.
2. Description of the Related Art
Various optical discs of different storage capacities such as a CD, a DVD, and a BD are available. A disc drive apparatus that performs recording and/or playback on such various optical discs is intended to rotate a loaded optical disc at an optimum rotation speed for the optical disc. In detail, in the case of performing recording or playback on an optical disc of a relatively small storage capacity such as a CD, it is sufficient for the disc drive apparatus to drive a spindle motor by low-speed rotation. In the case of performing double-speed recording or the like on an optical disc of a large storage capacity such as a BD, on the other hand, the disc drive apparatus drives the spindle motor by high-speed rotation. To support a wide variety of optical discs of different storage capacities, the disc drive apparatus desirably rotates an optical disc in a range of about 1000 rpm to about 15000 rpm. Further, rotation up to about 20000 rpm is expected in the future.
When rotating an optical disc at high speed, friction between the optical disc and the air in the apparatus body increases, as a result of which a torque in a direction opposite to a disc rotation direction due to air resistance, namely, a windage-loss torque, increases. Since a larger windage-loss torque occurs in an outer periphery of the optical disc, the optical disc may slip on a turntable that rotatably supports the optical disc. This makes it difficult to rotate the optical disc at a predetermined rotation speed, and also causes adverse effects on recording/playback characteristics.
Moreover, the optical disc is typically held on the turntable by magnetic attraction between the turntable and a chucking pulley. In many cases, an upper part of the optical disc is closed by an outer wall of an enclosure, whereas a lower part of the optical disc is open as an optical pickup driving region. Therefore, during high-speed rotation, an increase in pressure difference between the upper and lower surfaces of the optical disc may cause the optical disc to vibrate considerably, thereby inhibiting stable rotation. In addition to the vibration of the optical disc, because the upper part of the optical disc is relatively at a negative pressure, there is a possibility that the optical disc is drawn upward and as a result the chucking pulley becomes disengaged. Besides, when a force of attraction between the turntable and the chucking pulley is weak, the vibration of the optical disc during high-speed rotation further increases, making the chucking pulley more easily disengaged. Furthermore, the vibration of the optical disc causes vibration noise.
On the other hand, if the magnetic attraction force between the turntable and the chucking pulley is increased, upon ejection of the optical disc an excessive load is put on a driving mechanism in order to pull the turntable and the chucking pulley apart. Thus, there is a limit to the increase of the magnetic force.
Japanese Unexamined Patent Application Publication No. 2000-268459 is an example of related art.